Chemical weapons disable, injure, or kill by disrupting the normal physiological processes of their victims. They include lethal nerve, blister, blood, and choking agents; nonlethal incapacitating agents that induce temporary paralysis in their victims; and tear gas. Their means of delivery include missiles, tube and rocket artillery, aerial bombs, spray dispensers, and mines.
Although chemical weapons are usually classified as weapons of mass destruction, their destructive potential is significantly less than that of nuclear and biological weapons. Chemical agents must be used in massive quantities in order to attain lethal concentrations over broad areas. Their effectiveness depends on having the appropriate delivery means and the right atmospheric conditions (such as wind speed and air temperature).
Because the impact of chemical-agents can be significantly reduced through countermeasures, such as protective masks and overgarments, these types of attacks are most effective against military organizations or civilian populations that lack such protection.
Chemical weapons were first used on a widespread basis by both sides during World War I and were subsequently used by the Japanese in Manchuria in the 1930s; Egypt in Yemen in the 1960s; and, in the 1980s, by Iraq during the Iran-Iraq War, by Libya in Chad, and by the Iraqi government against Kurdish insurgents and civilians.
The United States and Russia retain what are probably the largest inventories of chemical-warfare agent in the world, although both countries are currently in the process of eliminating their stockpiles, in accordance with their obligation under the Chemical Weapons Convention. At present, there at 188 state parties to the CWC. Israel and Myanmar have signed, but not ratified the CWC, while Angola, North Korea, Egypt, Somalia, and Syria have not joined the convention. Several of these countries, including Syria, North Korea, and possibly Egypt, are believed to maintain chemical weapons stockpiles.
Until the early 1990s, Iraq had one of the largest chemical-warfare programs in the developing world. As a result of the 1991 Gulf War, the efforts of United Nations weapons inspectors in the decade following the war, and the decision of the Iraqi government to join the CWC in 2009, nearly all of Iraq's known chemical-warfare capabilities have been destroyed.
Iraq's use of chemical weapons during the Iran-Iraq War provided much of what is known today about chemical warfare and its long-term health effects. Experience during that war showed that large concentrations of agent are generally required to cause heavy loss of life, though even small amounts can injure thousands. Some 10,000 Iranians, half of them civilians, were killed by chemical weapons during eight years of fighting, and another 50,000 suffered moderate to severe injuries. More than 45,000 Iranians continue to suffer the long-term health effects of exposure to chemical agents, including skin, eye, and respiratory ailments, birth defects, cancer, and post-traumatic stress.
Two of the best-known Iraqi chemical attacks on civilian targets are the bombings of the Iranian town of Sardasht in June 1987 and the Iraqi Kurdish town of Halabja in March 1988. (The 25th anniversary of the latter attack was marked earlier this week.) In Sardasht, Iraqi aircraft dropped seven 250-kilogram bombs filled with mustard, killing about 100 people and injuring 4,500. In Halabja, more than 50 aircraft dropped some 200 bombs filled with mustard and nerve agents, killing some 5,000 immediately and injuring several thousand more.